This disclosure generally relates to a process for treating a hydrocarbon oil. More particularly, the process described herein is directed to upgrading a heavy oil feedstock by a supported hydroprocessing catalyst assisted hydrotreatment.
In general, crude oils range widely in their composition and physical and chemical properties. Heavy crude oils are typically characterized by a relatively high viscosity, low API gravity (generally lower than 25xc2x0), high concentrations of sulfur, nitrogen and metallic impurities and a high percentage of high boiling components. In the last two decades, environmental and economical considerations have required the development of processes to (1) remove heteroatoms such as, for example, sulfur, nitrogen, oxygen and metallic impurities, from the hydrocarbon oil feedstocks; and, (2) convert the hydrocarbon oil feedstocks to lower their boiling ranges. Such processes generally subject the heavy crudes or their fractions to thermal cracking or hydrocracking to convert the higher boiling fractions to lower boiling fractions optionally followed by hydrotreating to remove the heteroatoms.
Acidic compounds such as naphthenic acids are often present in crude oils and pose a serious problem in processing such crudes. Naphthenic acids are carboxylic acids having a ring structure, usually of five member carbon rings, with side chains of varying length. Such acids are corrosive towards metals and must be removed by, for example, treatment with aqueous solutions of alkalis such as sodium hydroxide to form alkali naphthenates. However, with increasing molecular weight, the alkali naphthenates become more difficult to separate because they become more soluble in the oil phase and are powerful emulsifiers.
The acid content of a hydrocarbon oil is measured by the total acid number or xe2x80x9cTANxe2x80x9d which is defined as milligrams of potassium hydroxide (KOH) necessary to neutralize the acid in 1 gram of oil. Typical refineries can process crudes having a TAN of up to 0.3. Some crude oils have TAN""s of more than 4.0, e.g., Mariner crude from the North Sea, making it difficult to process such heavy crude oils.
Processes for treating hydrocarbon oils are known. See, e.g., U.S. Pat. Nos. 3,622,500; 3,725,251; 3,761,393; 3,775,296; and 3,844,933. Each of these patents disclose processes which operate at high pressures and employ high concentrations of catalysts in the form of small particles.
Another example of a process for treating hydrocarbon oils is U.S. Pat. No. 5,928,501 which discloses a process employing a catalyst composition having high hydrogenation activity and being formed from a non-noble metal of Group VIII of the periodic table and a metal of Group VIB of the periodic table on a phosphorus-treated carbon support. However, several problems are associated with employing a carbon supported catalyst. For example, presently there exists no proven technology for regenerating a carbon supported catalyst after it has been substantially deactivated during the hydrotreating process. Thus, in order to continue the process, new carbon supported catalyst must be purchased since it is not possible to regenerate and therefore reuse the carbon supported catalyst after it has been recycled several times.
It would therefore be desirable to provide a process to upgrade heavy acidic hydrocarbon oils to simultaneously reduce acidity and increase API gravity thereby improving the marketability of the crude oil and increasing its value. It would also be desirable to operate the upgrading process at moderate pressures which would be more economical to set up and easier to operate. Furthermore, it would be desirable to employ a catalyst which can be regenerated resulting in a substantially longer cycle life and lower overall costs.
In accordance with the present invention a process for treating a hydrocarbon oil feed is provided which comprises:
a) forming a slurry which includes a heavy hydrocarbon oil and a catalytically effective amount of a hydroprocessing catalyst based on a catalyst support selected from the group consisting of alumina, silica-alumina, silica, titania, and magnesia;
b) introducing the slurry into a reaction zone in the presence of hydrogen; and,
c) subjecting the slurry to upgrading conditions to provide a hydrocarbon oil product having a lower acid number and increased API gravity wherein the concentration of the catalyst in the slurry is substantially the same as the concentration of the catalyst in the slurry present in the reactor and in the hydrocarbon oil product.
The term xe2x80x9cregenerablexe2x80x9d as utilized herein shall be understood as referring to those supported hydroprocessing catalysts which can be subjected to a known regeneration process thereby allowing the catalysts to be regenerated and then reused in the upgrading process. For example, in a typical regeneration process, the supported hydroprocessing catalysts are calcined at high temperatures, e.g., temperatures above about 450xc2x0 C., in air to burn off any impurities in the catalysts, e.g., coke deposits.
The foregoing process advantageously reduces (1) the acid number of the hydrocarbon oil feeds; (2) the viscosity of the hydrocarbon oil feeds; and, (3) the sulfur content present in the hydrocarbon oil feeds while also substantially increasing the API gravity. The content of asphaltenes, nitrogen and metallic impurities present in the hydrocarbon oil are also reduced. The product oil therefore contains significantly reduced concentration of residue (material boiling above about 524xc2x0 C.) compared to feed hydrocarbon oil.